Recently, a high-speed operation of semiconductor integrated circuit devices is being developed. The high-speed operation is realized by low resistivity of a wiring material or the like. Therefore, as for the wiring material, Cu having lower resistivity is used instead of aluminum that has been conventionally used.
Cu is not easily etched unlike aluminum. Thus, as for a technique for processing Cu wiring, there is used a damascene method for forming grooves in accordance with a wiring pattern in advance in an interlayer insulating film, forming a Cu thin film so as to fill the grooves, and chemically and physically polishing the Cu thin film by using a CMP method while leaving Cu only in the grooves.
Since, however, the damascene method has complicated processes, it is required to form a wiring by a dry etching technique as in the case of aluminum. As far a dry etching technique for Cu, there is suggested a technique for performing anisotropic oxidation on a Cu film and then dry etching the copper oxide thus formed by an organic acid (see, e.g., Japanese Patent Application Publication No. 2010-027788).
However, the technique described in Japanese Patent Application Publication No. 2010-027788 (JP2010-027788A) requires two steps including anisotropic oxidation and organic acid dry etching. In the case of etching a deep hole or trench, the anisotropic oxidation and the organic acid dry etching need to be repeated multiple times, which results in complicated processes. Since the Cu is oxidized and then etched by an organic acid, a high etching rate is not obtained. Further, a substrate needs to be heated during the organic acid dry etching, so that the apparatus configuration becomes complicated and a base may be damaged. Moreover, since a large amount of organic acid needs to be supplied, reaction efficiency becomes poor and by-products are easily produced.